Exploring plant growth promoting traits and biocontrol potential of new isolated Bacillus subtilis BS-2301 strain in suppressing Sclerotinia sclerotiorum through various mechanisms

Abstract

<i>Sclerotinia sclerotiorum</i> (Lib.) de Bary is the causative agent of stem white mold disease which severely reduces major crop productivity including soybean and rapeseed worldwide. The current study aimed to explore plant growth-promoting traits and biocontrol of new isolated <i>Bacillus subtilis</i> BS-2301 to suppress <i>S. sclerotiorum</i> through various mechanisms. The results indicated that the BS-2301 exhibited strong biocontrol potential against <i>S. sclerotiorum</i> up to 74% both in dual culture and partition plate experiments. The BS-2301 and its crude extract significantly suppressed <i>S. sclerotiorum</i> growth involving excessive reactive oxygen species (ROS) production in mycelia for rapid death. Furthermore, the treated hyphae produced low oxalic acid (OA), a crucial pathogenicity factor of <i>S. sclerotiorum</i>. The SEM and TEM microscopy of <i>S. sclerotiorum</i> showed severe damage in terms of cell wall, cell membrane breakage, cytoplasm displacement, and organelles disintegration compared to control. The pathogenicity of <i>S. sclerotiorum</i> exposed to BS-2301 had less disease progression potential on soybean leaves in the detached leaf assay experiment. Remarkably, the strain also demonstrated broad-range antagonistic activity with 70%, and 68% inhibition rates against <i>Phytophthora sojae</i> and <i>Fusarium oxysporum</i>, respectively. Furthermore, the strain exhibits multiple plant growth-promoting and disease-prevention traits, including the production of indole-3-acetic acid (IAA), siderophores, amylases, cellulases and proteases as well as harboring calcium phosphate decomposition activity. In comparison to the control, the BS-2301 also showed great potential for enhancing soybean seedlings growth for different parameters, including shoot length 31.23%, root length 29.87%, total fresh weight 33.45%, and total dry weight 27.56%. The antioxidant enzymes like CAT, POD, SOD and APX under BS-2301 treatment were up-regulated in <i>S. sclerotiorum</i> infected plants along with the positive regulation of defense-related genes (<i>PR1-2</i>, <i>PR10, PAL1</i>, <i>AOS</i>, <i>CHS</i>, and <i>PDF1.2)</i>. These findings demonstrate that the BS-2301 strain possesses a notable broad-spectrum biocontrol potential against different phytopathogens and provides new insight in suppressing <i>S. sclerotiorum</i> through various mechanisms. Therefore, BS-2301 will be helpful in the development of biofertilizers for sustainable agricultural practices.